This proposal will concentrate on the study of the mechanisms of interaction of heterologous tissues during odontogenesis. The specific aims can be summarized as follows: A. Experimental recombinations of epithelial and mesenchymal components of dental and non-dental embryonic tissues will be used to isolate and define specific populations of odontogenic cells. Any tissues capable of interacting to form tooth-like structures can be considered odontogenic. Differences in odontogenic and non-odontogenic tissues will be characterized using biochemical and ultrastructural techniques. B. The interaction of odontogenic tissues with natural (micro-dissected tooth matrix) and artificial (collagen/GAG) gels) collagenous matrices will be used to study the effect of specific extracellular matrix (ECM) macromolecules on cellular function and cytodifferentiation. C. Biochemical techniques (CM-cellulose chromatography of collagen chains and CNBr peptides and specific polysaccharidase assay of GAG) will be used to characterize the ECM macromolecules produced during odontogenesis in vivo and in vitro. If the ECM is found to affect the differentiation of ameloblasts or odontoblasts, it will be important to know the specific components of that matrix. D. Ultrastructural techniques, such as freeze-fracture and histochemistry, will be used to further characterize the ECM and the plasmalemma and cell surface of odontogenic and non-odontogenic cells. The information obtained will be used to evaluate the relative roles of cell-ECM and cell-cell interactions in organogenetic tissue interactions.